This application claims benefit of Japanese Patent Application No. 2001-014480 on Jan. 23, 2001, the contents of which are incorporated by the reference.
The present invention relates to portable telephone sets and, more particularly, to foldable portable telephone sets having two foldable housings interconnected by a cable.
In a prior art telephone set such as a foldable portable telephone set, when the set is in use for communication, radio signals are received by an exclusive receiving antenna and a transmitting/receiving antenna and transmitted via a cable to a radio circuit in which the better sensitivity one of the radio signals is demodulated.
FIG. 6 is a block diagram schematically showing a prior art foldable telephone set. Referring to the Figure, reference numeral 13 designates an upper housing, and reference numeral 14 designates a lower housing. These housings 13 and 14 are interconnected by coaxial cables 9a and 9b and a flexible circuit board 15. The coaxial cables 9a and 9b serve such that when an external antenna assembly such as a vehicle antenna assembly is connected to an external input/output terminal unit 11, radio signals received by the external antenna assembly are transmitted therethrough to the side of the upper housing 13. The flexible circuit board 15 supplies the power from a battery 12 to the side of the upper housing 13.
The upper housing 13 accommodates a radio circuit 2 for demodulating the radio signal to obtain a voice signal or the like and modulating voice signal or the like to to obtain the radio signal, a radio signal transmitting/receiving antenna 7, an exclusive radio signal receiving antenna 8, a control circuit 1 for controlling the timings of transmission and reception of radio signals and so forth, RF (radio frequency) connectors 5a and 5a′ interconnecting the coaxial cables 9a and 9b and the lower housing 14, GND (ground) terminals 6a and 6a′ provided between the RF connectors 5a and 5a′ and the coaxial cables 9a and 9b, and a flexible circuit board connector 16b interconnecting the flexible circuit board 15 and the lower housing 14.
The radio circuit 2 has an amplifier for amplifying the radio signals and an isolator for such purposes as preventing mixed modulation and the oscillation frequency stabilization.
The lower housing 14 accommodates a transmitting/receiving RF terminal 11a for inputting and outputting the radio signals from and to a transmitting/receiving antenna in an external antenna assembly connected via the external input/output terminal unit 11, an exclusive receiving RF terminal 11b for inputting radio signals from an exclusive receiving antenna in the external antenna assembly, RF connectors 5b and 5b′ interconnecting the coaxial cables 9a and 9b and the upper housing 13, a GND terminal 6c connected to the minus terminal of the battery 12, and GND terminals 6b and 6b′ provided between the RF connectors 5a and 5b′ and the coaxial cables 9a and 9b. 
The operation of the telephone set in the case of radio signal communication with the external antenna assembly connected to the external input/output terminal unit 11, will now be described. In this state, the operations of antennas 7 and 8 are effectively stopped.
A voice signal or the like is first passed for noise removal through a filter or the like and is then fed to the radio circuit 2. The radio circuit 2 modulates the inputted voice signal or the like to obtain a radio signal, and feeds out the radio signal at a timing instructed by the control circuit 1 via the RF connector 5a′ and the coaxial cable 9b to the side of the lower housing 14. On the side of the lower housing 14, the radio signal fed through the coaxial cable 9b is taken via the RF connector 5b′ to the inside. This radio signal is fed out via the transmitting/receiving RF terminal 11a to the external antenna assembly. The radio signal fed out to the external antenna assembly is radiated from the transmitting/receiving antenna therein to an opposite side telephone set or the like in the communication.
The radio signal radiated from the opposite side telephone set or the like is received by the transmitting/receiving antenna and the exclusive receiving antennas (not shown) in the external antenna assembly. The received radio signals are transmitted via the RF connectors 5b and 5b′ and coaxial cables 9a and 9b to the side of the upper housing 13. On the side of the upper housing 13, the transmitted radio signals are taken via the RF connectors 5a and 5a′ to the inside and fed to the radio circuit 2. The radio circuit 2 detects the better receiving sensitivity one of the input radio signals, and demodulates the better receiving sensitivity radio signal to obtain a voice signal or the like.
When the power supply to the telephone set is turned on, the charge outputted from the plus terminal of the battery 12 is supplied via the flexible circuit board connector 16b, the flexible circuit board 15 which mainly transmits control signals and the flexible circuit board connector 16a to the side of the upper housing 13. On the side of the upper housing 13, the control circuit 1 and the radio circuit 2 are activated and driven by the supplied power.
In the prior art technique as described above, however, two coaxial cables and so forth are used for the radio signal transmission between the two housings, and the radio signal transmitted via one of the two coaxial cables is not actually used for communication, which is undesired from the standpoint of efficient radio signal transmission between the two housings. In addition, in view of the reduction of the size, thickness and weight as desired for recent foldable portable telephone sets or the like, it is desired to preclude any wasteful coaxial cable.
Furthermore, while in the prior art technique a flexible circuit board or the like is used for the power supply from the battery, the flexible circuit board is readily affected by externally generated noise. Therefore, it is preferable to use other means for the power supply purpose.